Interesting, the only way to know if CPU PM is working is Intel Power Gadget. Without Nvidia GPU frequency, power and temp data, there is no "visible" way to know anything. It is clear Fermi and older used 4 thresholds for PM (macOS GPU PM default) while Kepler and newer uses 16 power states.
These are only my personal experiments on the hardware I have. I can't speak for what data Vit has:
So, I can estimate power usage by monitoring draw at my UPS (it has a built-in Kill-a-Watt-like feature), and I've established a baseline with and without certain hardware in Windows to get some idea of the System and GPU power state at any given time. I saw no change in power draw in macOS with vs. without the dAGPM.kext. So, that's where I get that result.
For temperature, I have no reliable tool from Nvidia in macOS comparable to Intel Power Gadget to really test it, but I do have kozlek's GPUSensor kext, which was fixed a few months ago to provide data for Pascal. I agree I have no way to validate the results I get out of that kext, but I saw no change in what it showed with vs. without the dAGPM.kext. Even if its data is inaccurate, it does change with load, so it is at least possible that if dAGPM.kext was improving power management I might see some difference. So, that's where I get that result.
In terms of performance, I saw no improvement in tests where I know the 104 driver has issues, such as web gl. It was at least theoretically possible that improved power management might bring improvement in the tests. It did not.
These are just some ways that changes in Nvidia GPU frequency, power, and temp might be observed, although I agree that none of this is as good as Intel Power Gadget is for CPU PM.
I'm not saying that dAGPM.kext and discrete graphics power management on Kepler+ is useless, and I don't think Vit is either. I'm just looking for a "visible" way to know anything. Do you have any suggestions?
Also, see here where I asked Vit about it:
https://github.com/lvs1974/NvidiaGraphicsFixup/issues/2
GPU PM has nothing to do with sleep (no native sleep mode). With GPU PM and without has nothing to do with black screens; invalid experiment. Off topic.
Also, thank you for clearing this up. I was also under the mistaken impression that GPU PM might help with sleep issues.